D-I-Y WASP Shell Pasting Machine?

I've found two motors I like - both NEMA 23 570 oz-in like the Super Stinger. One is a uni or bipolar motor but only has a 1/4" shaft (420 oz-in in unipolar mode). The other is bipolar only but has a 3/8" shaft. I like the idea of a unipolar as there's more controllers out there for them (and using a smaller drive wheel would compensate for the loss in torque) in case the one I found doesn't work satisfactorly, but 1/4" is getting kinda spindly - I'd prefer a 3/8" shaft. What are your thoughts - do you think the 1/4" would be hefty enough?

Time to make a realistic decision what you want to do with this. If you don't own a fireworks business, how many 12 inch shell do you think you'll make in a year? If the answer is more than 2, you probably should buy a real WASP, since the cost of making experimental 12s to get your own algorithms right will be way more than the cost of the equipment. Be realistic about the size of the motors you need, since this affects everything to do with the construction. The weight of a shell varies with the cube of its diameter, so a 12 inch is 27 times heavier than a 4 inch and 64 times heavier than a 3. So if 570 oz-in motors with 4 inch drive wheels can handle a 12, then you would get the same performance with 11 oz-in motors on 2 inch drive rollers with a 4" (21 oz-in for a 5", 36 oz-in for a 6"). Also bear in mind that the maximum torque is only possible if the drivers can deliver the maximum current, which is likely to be in the region of 15A per phase for big motors. My proto used motors with 1/8 inch shafts delivering 44 oz-in at a modest 1.2 amps per phase.

6 - 8" would be for special things like kamuros and stuff and probably only a handful a year.

That's a pretty big size range and if it's not practical I can drop off the bottom or top end and be well satisfied with 3-4-5-6" capability.

The only real complaint I've heard on these machines is stalling of the motors, especially on Stinger units converted to Super Stingers. It seems the conversion is usually just longer arms but the motors are not upgraded. In fact it seems the original Super Stinger units had lower torque motors and were quickly upgraded to the 570 oz-in (5 amp) units they now use (which as near as I can tell are the highest torque NEMA 23 motors available).

The 570 oz-in motors aren't that expensive, in the $(US)50 range so we're talking about a less than $100 savings by user weaker motors, probably more towards $50 but when you figure in a stronger power supply for the stronger motors it pushes up to around $100.

In the scope of the project that's not a whole lot.

My thoughts are to duplicate a working, proven design with as many off the shelf parts or easily fabricated parts as possible so the average Joe can build this. After we have a set of plans drawn up, parts sources found and software working then I fully expect the project to continue to evolve. I'm hoping the PIC or even BASIC STAMP people will take note and maybe eliminate the need for a pc for us and I'm certain many will start to tweak on the frame to make it smaller and more portable . . . or maybe make it convertible, i.e. a small compact frame for smaller shells but one that could easily be expanded for larger shells by installing longer arms and stuff when larger shells demand it.

As far as tweaking the algorithm for larger shells - is it really any different than tweaking it for smaller ones? Rather than waste shells on practice taping runs wouldn't we be better served by duplicating what Ned did by making dummy shells, spray painting the outside with flat white paint and installing a pen in place of the tape so we can trace out the taping pattern and tweak as needed until we get something we like?

A brief project update - I've found a WASP owner who is willing to take measurements, pictures, do some drawings, etc. for us. Like all of us, he's busy too though so I can't give a definite date but some frame plans ARE in the works, stay tuned!

The bent sheet metal that makes the spring on the right hand bearing block may be an issue for a home fabricator. It may not be necessary and it's not used on the WASP Mini, but a method to home brew it is in the attached picture from a video I found on YouTube.

Things are moving, CADs are being created and we've found some help with the software. Our CAD drawer has just been busy so he's not got as much done as he'd like and I've been swamped with work and my son's wedding lately. Our software person is just waiting on us to get a frame up and working so he can start playing with software.

I can help with the building part as a mate works at a lazers metal cutting place and if we can get the messurements of the part's required I can get them cut and maybe get the extruded aluminum t-slot framing free as the amount of off cuts they scrap is amazing.

After a long hiaturs I'm back to this project. Life just got busy with some crazy overtime at work.

The motor drive rollers - McMaster-Carr supply carries some 4" finned drive rollers but their minimum shaft diameter is 3/4" so a bushng would have to be used for most stepper motors. FixtureWorks.com also carries finned drive rollers and they carry them in a wide variety - including 2" diameter instead of 4" which I thnk more closely matches what Peret suggested. I'm wondering what material would be best - neoprine or urethane? And what hardness rating. Peret, if you have time would you mind taking a look at fixtureworks.com and seeing if you can spot something you think would be appropriate?

I took a quick look, but all of them have a large internal diameter, so you would have to make a drive adaptor. While you're doing that you may as well make the entire roller. 1.75 inch diameter drum with 1.875 flanges on the end, 2 inches between flanges, center drill to suit your motor shaft. Radial drill and tap holes for set screws to secure it to shaft, fill between flanges with #223 neoprene O rings. I think I specified #224 before but in practise they were found to slip a bit. For the idler, nothing seems to work as well as McMaster Carr 2497K3 teardrop roller. Use a soft one.

I've been looking all over the place here in the UK for the 25mm-50mm extruded T slot aluminum with no luck as of yet, so if anyone is going to the US for there holidays soon put a few lengths of 2"-!" in your luggage please lol.